An interposer module (also called an interposer wafer) is used to bridge or connect multiple devices, chips or wafers to a substrate. Designing an interposer module is difficult because the interposer module needs to account for different sized and shaped devices having different topologies. Heterogeneous integration requires the interposer module to incorporate different sized and shaped devices that generally have different topologies. For example, the difference in device heights makes the design of the interposer module challenging because the designer needs to adjust the vertical topology of the interposer module to be exactly matched with the device heights. This requires accurate control of the fabrication process.
In addition, the interposer module has limits in selecting bonding methods and requires multiple bonding. Heterogeneous integration generally requires multiple bonding processes. The bonding process becomes more frequent as the number of devices increases. The difficulty becomes more challenging when the devices are stacked in a three-dimensional (3D) orientation.
Existing interposer modules have several drawbacks. For example, the different device topologies have different device heights making it difficult to properly integrate the devices. To modulate the different heights, prior methods involved stacking bump materials or using bonding methods that compress bonding material. However, both methods are difficult because these methods do not allow for accurate control of the fabrication process. Furthermore, even though the device topologies for integration can be adjusted or involves identically designed devices, the device topologies can be diverse because of fabrication variations. This diversity cannot be controlled and the process should be designed to compensate for the unpredictable difference in wafer surface profile, material deposition thickness, material etching rate, wafer bowing, etc.
Another drawback is the number of different bonding processes required for the different devices. Typically, as the number of devices increase, so does the number of bonding processes. The multiple bonding processes involve different bonding steps, materials and conditions such as temperature, pressure, voltage, etc. The sequence of bonding processes should be carefully designed and controlled so that latter bonding methods do not damage former bonding materials and former bonding methods do not generate any issues to disturb the latter bonding conditions. The multiple bonding processes also generate several thermal cycles, which can produce problems such as device stress, wafer bowing, material oxidation, inter-material reaction, outgasing, and material damages.
In some situations, the devices need to be encapsulated to protect them from damage or contamination created by dust, debris, particles, humidity or chemicals. Some applications need a hermetically sealed vacuum package to improve device performance and reliability. These goals are generally achieved by employing additional wafers that cap the devices, which, however, increase fabrication complexity and cost and produce yield problems.
The above drawbacks provide challenges to designers of interposer modules. Thus, there is a need for an interposer module that overcomes the above drawbacks.